Fire-damp indicator



Dec. 13, 1927.

O. MARTIENSSEN FIRE DAMP INDICATOR Filed March 8, 1924 @RM- v 'Patented Dec. 1.3, 1927.

UNITED STATES `osent MARTIENSSEN,

FIRE-DAM? Application led March 8, 1924, Serial No.

This invention relates to yfire-damp indicators and its object is to produce apparatus of this kind which -is entirely safe and certain in operation. A

The arrangement of a good lire-damp indicator should be such that an admixture of 2% methane in the air may be noticed with certainty in order that precautionary measures can be taken before an'explosive mixture of 5% exists. Another desideratum is that the fire-damp indicator should be made in the form of an easily transportable, strong and simple instrument which may be used by the miners in coalmines at their work. These objects are diiiicult to. accomplish on account of the great inactivity of methane both "in a physical and chemical sense. Although there are a great number of laboratory appliances for indicating the smallest uantities of methane, safe appliances suita le for use in mines have not hitherto become known.

In accordance with the present invention the drawbacks in known apparatus are overcome by employing for the indication of methane very simple but entirely novel means which consists in irst converting the methane into a substance whose existance can be more easily perceived chemically The methane is most easily converted by burning it. As is well known a complete combustion may be accomplished by placing a glowing platinum wire into the gas mixture that contains the methanel course, precautionary measures must be'V taken to prevent the occurrence of an exp'losion in the apparatus itself through said combustion. These measures consist in causing the combustion to take place in a chamber into which the gas mixture is obliged to enter through a porous stone.v By this means all risks o an explosion are recluded. By this combustion in the com ustion chamber one part of methane and two parts of oxygen give two arts of water and one part of carbonio aci gas. For'determining the carbonio acid gas producedand for ascertaining therefrom the composition of the gas mixture various means and methods may be employed.

In accordance with the present invention the carbonio acid gas and the water vapour are absorbed in the wellknown manner by potash solution or a similar substance and or XIEL,'GERMANY. I

mmca'ron.

697,972, and in Germany March 26, 1923.

the lowering of the pressure due to this absorption is used for measuring the quantity Y of gas absorbed and thus the quantity of methane burned. In order that this alteration of pressure may be considerable and that the change of the methane content to an extent of one per cent may be capable of measurement, it is necessary for the porosity of the stone to be very small. This porosity should only be s'ulicient to allow a quantity of gas mixture to enter that is completely burned by the wire and under these conditions a constant lowering of pressure during the continuous combustion will be obtained in the combustion chamber.

In a re-damp indicator of this kind a diliiculty is however encountered in that the wire at which the combustion takes place tends vto' become fragile. This is due to the fact that any material which on the whole may be suitable for the purpose such as platinum, is liable when heated to orm compounds with the carbon liberated during the combustion of methane. The use of a thicker wire to overcome this drawback is not feasible because this would entail the use of a larger battery of accumulators (such as shown at K in Figures 2 and 3) which would make the apparatus cumbersome. andphysically, and in indicating the prqsence of said substance by the apparatus.

This diilicultyis overcome by the present invention through coating the Wire with a thin layer of ceria or some other suitable oxide which prevents the wire from combining with carbon, but which does not interfere with the combustion of the methane by the glowing` wire.

Another means of making the wire less liableto break consists in preventing the wiremgtom being heated in the' first instance to a needlessly high temperature. Ex eriments have shown that a sufficient coin us'- tion of methane takes place if the Wire is heated only to a bright red heat, but that' a deterioration of the wire by the absorpcontinue in the external atmosphere and give rise to a tire-damp explosion. To obviate this the apparatus is enveloped in an external chamber whose walls partly consist of stone which is very pervious to gas.. It

has been found that a gas mixture which is generall hio'hly explosive, when ignited in sucha c amber, does not produce an explosive effect and does not give rise to a continuous flame.

My invention is illustrated in the accompanying drawings, in which,

Figure l represents a central vertical section thru an apparatus of the character contemplated;

Flgure 2 is a vertical section of another embodiment of my invention; and

Figure 3 is a Wiring diagram of the electric circuits for parts represented in Figure 2.

Referring to Figure 1 of the drawings, A is a cylindrical wall closed at both ends by walls B consisting ot' very porous stone. The stones B thru which the mine gases enter the housing of the tire damp indicator, may be such highly porous stones as those generally known as sponge stone. These porous stones ma be made of clay fired without glazing. urimir the kneading process, however, sawdust or other suitable filler is added, such saw-dust being consumed during the firing operation in such a way as to produce. a highly porous product. A substitute for the above described sponge stone may be had by sintering together coarse granules of glass, which. during the sintering operation, fuse together slightly to form a porous mass.

In order to give an idea as to the degree of orosity of the stones used in accordance witi the application it may be stated that cigar smoke may be blown thru them without noticeable resistance. The smoke jet is hardly dispersed by the stone. It such a stone is held over a gas burner, the gas burns without difiiculty above the stone as soon as it is lighted above the stone. The flaring back of the flame, however, such as is pos. sible in case of an ordinary wire netting, is not possible with the stone. If there is a mixture of air and methane in a chamber of this kind and the methane admixture amounts to about 7% a white hot wire may be placed in the chamber without the slightest noticeable eiectbeing produced. The methane burns steadily at the incandescent wire and the air and methane are converted into water and carbonio acid gas without any flame and Without a rise of pressure. If the methane content is 7 to 11% and the platinum wire is brought to incandcs'cence by means of a battery K (see Figure 3), a small bluish llame is formed fora moment but the flame immediately disappears again without any further visible result. This seuence of events in the container C is due to tie fact that the very porous stone walls B at opposite ends of housing A do not allow of suchy rises of pressure as are necessary for the production of explosive ignitions of vas mixtures in said container. On the other hand the products of combustion, particu* larly the carbonio acid, can only pass through the stone G so gradually that an incipient flame becomes extinguis ed immediately and thus obviates any continuous flash. In consequence the walls of the container C do not become hot as does the wire netting in a Davy safety lamp under similar conditions.

Enclosed in the housing A, B is a container C of metal to the bottom of which is connected a thick-walled glass tube H. The other end of this lass tube terminates in a Wide extension or c amber D, which is closed by a very porous stone E. The glass tube includes a U-shaped bend H which contains an indicating medium in the form of colored water column F or the like. The top of the container C has an opening which is blocked by a piece of stone G of relatively little porosity. Beneath the inlet or window covered by the stone G. is a platinum helix P which is adapted to be heated sulciently by current from accumulator K to bring about a conversion of the methane and air. The s acc beneath the helix in the containerV C is illed `b a body Q that contains a substance such as potash solution that absorbs carbonio acid gas and Water. It should be noted that the stone G above the platinum spiral P is comparatively dense, whereas the stone E which closes the enlarged portion D of the pressureA gauge tube (to be hereinafter referred to), has the same property as the lirst mentioned stone B, namely, high porosity. The relatively high and low degrees in porosity as between the stones G and E, is for the purpose of building up a pressure diference after the methane has been consumed on the platinum spiral and after the carbon dioxide an'd water formed during combustion have been absorbed, said pressure difference being readable along the branches of the U-shaped gauge tube.

If an apparatus of this kind is placed in air mixed with methane, the liquid F in the two limbs of the U-shaped indicator tube will remain at the same levels if the air does not contain more than one to two percent carbonio acid as But if the latinum helix P is marge to glow the met lane entering the container C through the porous stone G will be burned at the wire and the carbonio acid gas and water then formed will be absorbed by the Apotash solution in the body Q.. Consequently a lowering of the pressure in the container C with respect to the external atmosphere will take place and the liquid in the left hand "tube will. rise. The difference of the heights of the liquidsl in the limbs of the glass tube is a measure of the content of methane in the air. If the methane content is greater than 3% and the platinum helix is only heated after the a1.-

paratus has been brought into the atmosphere containing this amount of methane, an explosion will. occur in the container C which will be more or less violent according to the ainount of methane present and which will press the liquid upward in the right hand limb of the tube at the moment the platinum wire is heated. The liquid in the right hand limb however immediately drops again and rises in the left hand limb to an extent corresponding to the content of methane in the air.

The highly porous stone E vwhich allows suihcient gas to penetrate into the space D to maintain a pressure iii the same equal to that of the surrounding atmosphere also serves to restrict the explosion to the chamber D when the latter is too violent in the container C and consequently expels the liquid entirely from the tube F. In such cases the methane burns quietly in the chamber D. The carbonio acid gas formed during the combustion prevents the entrance of further oxygen and causes the flame to extinguish in a fraction of a second. no heating of the stone E occurs and the combustion does not extend to the content of the chamber A. This can only happen iii cases in which the inner parts of the apparatus are injured, but in such cases the same events occur in the chamber. A which have liust been described in connection with the chamber' D and the stones B render a propagation of the explosion to the surrounding atmosphere impossible.

Referring now to Figures 2 and 3, my improved tire-damp indicator with its battery may be embodied in the form of portable apparatus somewhat similar toan electric mining lamp. According t0 this .einbodiinent of my invention, an accumulatorK has its positive pole connected at l to a coiiductor comprising branches 2 and 3 leading, respectively, to a platinum helix P andan electric lamp L, said platinum helix and electric lamp as well as the negative pole of accumulator K, being grounded in themetal frame of the fire-damp indicator. Switches 4 and 5 may be included in branches 2 and'3 of the conductor, said switches being operated by knobs I and II for controlling the energizing of these elements. As shown in Figure 2, a. cylindrical wall A is. surmounted by a dome B of porous material. A metal container C is arrangedwithin said dome B said container being charged with a 1 mass Q which absorbs carbonio acid'gas andl water. The top wall of container C is provided with an opening covered by a stone slab G of low porosity similar to that shown in Figure 1. A U-tube indicator F ,has one branch thereof connected up with container C', the other branch of said U-tube being connected up to a widened extension'ehamber D which is closed above by a porous Hence stone E. It will be understood from this description that the .battery employed in energizing helix P', may also be used for supplying current to the lamp L so that the entire apparatus will forni a combined liredamp indicator and mine lamp.

I claim l. In a` tire-damp indicator, a container provided with an inlet-openiiig, means for continuously admitting a restricted quantity of a combustible gaseous `mixture to said container, means within said container for completely burning the gaseous mixture admitted thereto, means arranged within said container for absorbing, continuously, the products of combustion due to the burning of said gaseous mixture, a chamber vopen to v the pressure of the surrounding atmosphere, and pressure-responsive means connected up to said container and chamber for indicating the difference in pressure therein due to the continuing absorption of combustion products by said absorbing means.

2. In a fire-damp indicator, a container provided with an inlet-opening, a, 4closure for said inlet-opening, said closure being adapted to admit only a limited amount of a combustible gaseous mixture to -said contaiiicr, means within said container for burning` the gaseous mixture admitted thereto,

means arranged within said container for absorbing products of combustion derived from the burning of the gaseous mixture, a

chamber provided with a closure adapted to,

permit i'ree passage of the gaseous mixture but to prevent the passage of flame, and a differential pressure gauge connected to said container and chamber for indicating the methane content by the absorption of com-` bustion products derived fromsaid gaseous mixture.'

3. In a lire-damp indicator, the combina-` tion with a container provided with means for admitting a limited flow of gaseous mixture, a liot Wire within said container, an

electric accumulator connected up toisaid hot wire for completelyburning a combustible gaseous mixture admitted. to said container,

a body of absorbent material arranged within -v l said container for absorbngtheproducts of combustion due to the burning of said vgaseous mixture,- a chamber open to the pressure of the surrounding atmosphere, and a U- shaped gauge-tube having itsbranches connected respectively to said container and chamber, rsaid gauge-tubeb eing provided.

with a liquid column 'lj'or indicating the difference in pressures due to the absorption of combustion products byfsaid absorbing body.

4. In a fire-damp indicator, a container '1- provided withv an inlet-opening, a closure for saidv inlet-opening having a relatively low degree of porosity for limiting the amount of a combustible gaseous mixture vadmitted to said container, means within said container ico I I irs for burning the gaseous mixture admitted thereto, means arranged within said con'- tainer tor absorbing the products ot' combustion due to the burning ot the gaseous mixture, a chamber provided with a closure having a relatively high degree oit porosity, and a pressure gauge connected at one end to said containerl and at its other end to said chamber, said gauge being` proi'ided with means tor indicating the dillerence in pressure between said container and said chainber due to the combustion of gaseous mixture and the absorption ot combustion products by said absorbing means.

5. In a lire-damp indicator, a container provided with an inlet-opening, a closure for said inlet-opening` haring a relatively low degree ot porosityY 'l'or limiting the amount ot a combustible gaseousI mixture admitted to said container, a hot wire. within said container tor burning gaseous mixture admitted thereto, said wire being provided with a. ceria oxide coating, a battery lor energizing said wire, means for absorbing products ot' combustion due to the burning ot gaseous mixture, a chamber provided with a closure having a relatively high degree o't` porosity, and a gauge connected at one end to said container and at its other end to said chamber, for indicating the difference in pressure between said container and said chamber.

G. In a fire-damp indicator, the combination with a' coitainer, having an inlet l'or gaseous mixture, said inlet being provided with a porous closure for restricting the in gress of gaseous mixture and the egress ol'v products of combustion, ot a hot wire arranged within said container for burning a combustible gaseous mixture admitted to said container thru said closure, said hot wire being coated with ceria to prevent the formation of carbon compounds between elements of said wire and gaseous mixture, Inaterial within said container for absorbing products of combustion, said absorbent material being capacitated to continuously and completely absorb the products ot combustion derived from the gaseous mixture burnt by said hot wire, and pressure-responsive means 'for measuringr the decrease in pressure ot the gaseous mixture in said container due to its combustion and the absorption of said products ot combustion.

7. In a lire-damp indicator, the combination with a housing having an inlet-opening provided with a closure of material having a relatively high degree of porosity, of a container arranged in said housing, said con.- tainer having an inlet-opening provided with a closure constructed ot material haviagiij a relatively low degree of porosity, means in said container for burning a combustible gaseous mixture admitted thereto, means in said container t'o'r continuously and completely absorbing the products of combustion due to the burning of said gaseous Inizi-4 ture, a tube connected to said container, said tube having a portion of enlarged cross section forming a chamber with an opening conui'iunirating with the interior of said housing, a closure for the opening in said chamber and constructed of material having a relativelyv high degree of porosity, said tube being provided With a Ubend interposed between said container and chamber, and a liquid column in said Ubend for indicating the difference in pressures therein due to the combustion ot gaseous mixture and consumption ot' products ol combustion in said container.

In testimony whereol'v I affix my signature.

OSCAR MARTIENSSEN. 

